The present invention relates to the field of medical imaging and has particular applicability to computed tomography (CT). The invention also finds application in the fields of x-ray detection and imaging, including industrial inspection systems, non-destructive testing, baggage inspection, and the like.
Early CT scanners had only a single pencil beam x-ray source for transmitting x-rays through an examination region and a single detector for receiving attenuated x-rays after they had passed through a patient in the examination region. The source and detector were repeatedly rotated and translated about the examination region to obtain an image of the patient. The process of obtaining images with these scanners was slow and resulted in low resolution images.
Subsequent developments in CT technology have been made to decrease scanning time, increase patient throughput, and increase spatial resolution of images. These goals have been accomplished by, among other things, increasing the size of the beam radiation generated by the x-ray source and by increasing the number of detectors in a scanner.
As with the early scanners, second generation scanners used a rotation-translation system, but improved on the data acquisition speed of the earlier scanners through the use of an array of detectors and a small fan-beam x-ray source.
Third generation CT scanners also used a fan-beam x-ray source and an array of detectors that rotated simultaneously about the subject. However, the fan-beam of the third generation scanner was wide enough to cover the cross-section of a region of interest of the patient. Therefore, there was no need to translate the source-detector assembly.
Like the third generation scanners, fourth generation CT scanners used a fan-beam x-ray source that rotated about the examination region. However, the detectors were distributed around the examination region and did not rotate with the x-ray source.
Regardless of the configuration, CT scanners included at least one discrete radiation detector which converted x-ray radiation which traversed the patient examination area into electronic signals. Each radiation detector included a x-ray sensitive face, such as a scintillation crystal, which converted the received radiation into a corresponding quantity of light. A solid state photodiode was provided to convert the light emitted by the scintillation crystal into analog electrical signals indicative of the intensity of the crystal emitted light, hence the intensity of the received radiation.
In the case of multi-slice imaging, a two-dimensional array of radiation detectors was used. The radiation detectors were separately arranged on a circuit board. Each circuit board supported an array of photodiodes and attached scintillation crystals. In addition, a preamplifier was operatively connected to the circuit board and connected to each photodiode output to convert the photodiode current to an appropriate voltage within the dynamic range of the analog-to-digital conversion system.
The analog signals from the circuit board were carried to a separate processing area where they were converted from their analog state into a corresponding digital signal. The processing area was typically located some distance from the detectors. The analog signals were carried to the processing area via a relatively long bus system which extended from the photodiode to the analog-to-digital converter.
One problem with such a system relates to degradation of the analog signals as they travel over the long bus system between the radiation detectors and the processing area.
CT scanners operate in an environment of extraneous radio frequency electromagnetic signals, the frequencies of which vary over a wide band. Sources of extraneous signals include nearby operating electrical components, equipment, signals from other detectors, and the like. The long bus systems include long lead wires which inadvertently act as antennas in picking up extraneous electromagnetic signals and converting them into analog signals. The extraneous analog signals are superimposed on and mix with the analog signals from the detectors. The superimposed extraneous signals appear as noise and fictitious data when reconstructed into images. The resulting images are degraded by noise, ghosting, and other artifacts.
Another problem relates to the complexity of the electronic circuitry associated with the detectors as the number of detectors increased.
Each detector normally required a separate channel with all of the front end electronics and hardware to support the detector. As the number of detectors increased, the circuitry and associated electrical connections required to process and transfer the signals generated by the detectors increased as well. Therefore, implementing a large numbers of detectors has been a difficult task.
Those skilled in the art will, upon reading and understanding the appended description, appreciate that aspects of the present invention address the above and other matters.
In accordance with one aspect of the present invention, a computerized tomographic imaging system is provided. The system includes a stationary gantry portion defining an examination region and a rotating gantry portion for rotation about the examination region. An x-ray source is disposed on the rotating gantry portion for projecting x-rays through the examination region and a plurality of modular radiation detector units are disposed across the examination region from the x-ray source. Each radiation detector unit includes an array of x-ray sensitive cells for receiving radiation from the x-ray source after it has passed through the examination region and for generating an analog signal indicative of the radiation received thereby. Each radiation detector unit also includes a plurality of integrated circuits connected to the x-ray sensitive cells with each integrated circuit including a plurality of channels. Each channel receives the analog signal from an x-ray sensitive cell and generates digital data indicative of the value of the analog signal.
In accordance with a more limited aspect of the present invention, each modular radiation detector unit also includes a circuit board and the plurality of x-ray sensitive cells and plurality of integrated circuits are disposed on the circuit board.
In accordance with a more limited aspect of the present invention, the integrated circuits are disposed on the circuit board so that the variability of the distances from the x-ray sensitive cells to their respective integrated circuits is minimized.
In accordance with a more limited aspect of the present invention, each integrated circuit includes at least thirty-two channels.
In accordance with a more limited aspect of the present invention, each channel includes a ratiometric current to frequency converter which generates a number of electrical pulses during a time period, the number of pulses being proportional to the magnitude of the analog signal.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, each channel comprises a parallel to serial converter, the parallel to serial converter including means for interconnecting the channels so that the digital data from a plurality of the channels are combined to form a single output stream of digital data.
In accordance with a more limited aspect of the present invention, the array of x-ray sensitive cells is an array having M rows and N columns, M and N being integers greater than or equal to two.
In accordance with a more limited aspect of the present invention, each row of the array of x-ray sensitive cells corresponds to a single slice of image data.
In accordance with a more limited aspect of the present invention, at least one row of x-ray sensitive cells is connected to one of the integrated circuits.
In accordance with another aspect of the present invention, a CT imaging system is provided. The CT imaging system includes a gantry defining an examination region and an x-ray source for projecting x-rays through the examination region. The system also includes a plurality of x-ray sensitive cells for converting x-rays that pass through the examination region into a plurality of analog signals. A plurality of integrated circuits are in electrical connection with the x-ray sensitive cells and each integrated circuit receives the analog signals and generates digital data indicative of the values of the analog signals. The integrated circuits are disposed at the perimeter of the examination region and include means for interconnecting the integrated circuits so that the digital data from a plurality of the integrated circuits are combined to form a single output stream of digital data.
In accordance with a more limited aspect of the present invention, each integrated circuit also includes a plurality of channels with each channel having an analog to digital converter for converting the analog signal of a single x-ray sensitive cell to digital data.
In accordance with a more limited aspect of the present invention, each channel also includes a ratiometric current to frequency converter for generating a number of electrical pulses during a time period. The number of pulses are proportional to the magnitude of the analog signal.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, the CT imaging system also includes means to assure that the value of the first digital value is at least two.
In accordance with a more limited aspect of the present invention, each channel also includes a parallel to serial converter for outputting the digital data in a serial output stream.
In accordance with a more limited aspect of the present invention, the CT imaging system also includes a plurality of circuit boards disposed at the perimeter of the examination region and the x-ray sensitive cells and the integrated circuits are disposed on the circuit boards.
In accordance with another aspect of the present invention, a CT imaging system is provided which includes a stationary gantry portion, a rotating gantry portion for rotation about an examination region, an x-ray source disposed on the rotating gantry portion for projecting x-rays through the examination region, a plurality of x-ray sensitive cells disposed across the examination region from the x-ray source for receiving x-rays originating at the x-ray source and generating analog signals indicative of the x-rays received thereby, and at least one integrated circuit disposed in proximity to the x-ray detectors. The integrated circuit includes a plurality of channels with each channel coupled to a single x-ray sensitive cell for receiving the analog signal from the cell and for generating digital data indicative of the value of the analog signal.
In accordance with a more limited aspect of the present invention, the plurality of x-ray sensitive cells and the integrated circuit are disposed on a circuit board.
In accordance with a more limited aspect of the present invention, the plurality of x-ray sensitive cells are arranged in a two-dimensional array.
In accordance with a more limited aspect of the present invention, the two-dimensional array includes at least two rows and at least two columns of x-ray sensitive cells.
In accordance with a more limited aspect of the present invention, each channel includes a ratiometric current to frequency converter which generates a number of electrical pulses during a time period, the number of pulses is proportional to the magnitude of the analog signal received by the channel.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, each channel includes a parallel to serial converter for outputting the digital data of a plurality of x-ray sensitive cells in a serial output stream.
In accordance with a more limited aspect of the present invention, the integrated circuit also includes means for receiving digital data from a second integrated circuit. The received digital data is indicative of the values of the analog signals of the second integrated circuit. The integrated circuit also includes means for sending digital data to a third integrated circuit, the sent digital data being indicative of the values of the analog signals of the integrated circuit.
In accordance with another aspect of the present invention, a computerized tomographic imaging system is provided. The CT imaging system includes a stationary gantry portion having an examination region and a rotating gantry portion for rotation about the examination region. The system also includes an x-ray source mounted to the rotating gantry portion for projecting x-rays through the examination region and a plurality of radiation detector units disposed across the examination region from the x-ray source. Each radiation detector unit includes a circuit board and x-ray detector means for generating analog signals indicative of radiation that passes from the x-ray source to the radiation detector unit. The x-ray detector means includes a two dimensional array of x-ray sensitive cells and is disposed on the circuit board. Each radiation detector unit also includes multi-channel analog to digital conversion means for converting the analog signals to digital data. Each channel of the multi-channel analog to digital conversion means is connected to a single x-ray sensitive cell and the multi-channel analog to digital conversion means is disposed on the circuit board.
In accordance with a more limited aspect of the present invention, each channel includes a ratiometric current to frequency converter for generating a number of electrical pulses during a time period. The number of pulses is proportional to the magnitude of the analog signal.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, each channel includes a parallel to serial converter for outputting the digital data of the two-dimensional array of x-ray sensitive cells in a serial output stream.
In accordance with a more limited aspect of the present invention, each array of x-ray sensitive cells includes a number of rows and a number of columns and each row corresponds to a single slice of image data.
In accordance with a more limited aspect of the present invention, the multi-channel analog to digital conversion means includes at least one integrated circuit and the x-ray sensitive cells of one row of the array of x-ray sensitive cells are connected to the same integrated circuit.
In accordance with another aspect of the present invention, a method of computerized tomographic imaging is provided. The method includes projecting x-rays through an examination region using an x-ray source and detecting the projected x-rays after they have crossed the examination region using a plurality of x-ray sensitive cells disposed on a circuit board. The plurality of x-ray sensitive cells each generate a corresponding analog signal indicative of the x-rays detected thereby. The method also includes converting the analog signals to digital data using at least one integrated circuit. The integrated circuit includes multiple channels for analog to digital conversion of the analog signals and is disposed on the circuit board. Each channel converts the analog signal of a single x-ray sensitive cell.
In accordance with a more limited aspect of the present invention, the method of CT imaging also includes the step of generating a serial data stream including the digital data from a plurality of x-ray sensitive cells with the step of generating a serial data stream being performed using the integrated circuit.
In accordance with a more limited aspect of the present invention, the step of converting the analog signals to digital data includes, for each x-ray sensitive cell, storing a first value representing a number of pulses during a time period, the pulses occurring when the analog signal from each cell reaches a threshold value, and storing a second value indicative of the time between a first pulse and a last pulse that occur during the time period.
In accordance with a more limited aspect of the present invention, the method of CT imaging also includes the step of assuring that at least two pulses occur during the time period.
In accordance with another aspect of the present invention, a method of CT imaging is provided which includes rotating an x-ray source about an examination region, projecting x-rays through the examination region using the x-ray source, and detecting the projected x-rays using a plurality of two-dimensional arrays of x-ray sensitive cells. The arrays of x-ray sensitive cells is disposed on a plurality of circuit boards with each x-ray sensitive cell generating an analog signal indicative of the x-rays detected by the cell. The method also includes the step of generating digital signals indicative of the analog signals using a plurality of integrated circuits. The integrated circuits are disposed on the circuit boards and each integrated circuit includes a plurality of channels with each channel converting to digital the analog signal from not more than one x-ray sensitive cell.
In accordance with a more limited aspect of the present invention, the method of CT imaging also includes the step of generating a single output stream of the digital data by interconnecting the channels of the integrated circuits.
In accordance with a more limited aspect of the present invention, each channel of the integrated circuits includes a ratiometric current to frequency converter.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter for generating a number of electrical pulses during a time period. The number of pulses is proportional to the magnitude of the analog signal.
In accordance with a more limited aspect of the present invention, the method of CT imaging also includes the step of generating a first digital value indicative of a number of electrical pulses during the time period and second digital value indicative of a period of time between a first pulse and a last pulse occurring during the time period.
In accordance with another aspect of the present invention, a modular radiation detector unit for use in computerized tomographic imaging is provided. The modular radiation detector unit includes a circuit board and a plurality of x-ray sensitive cells disposed on the circuit board. The x-ray sensitive cells receive x-rays after the x-rays have passed through an examination region and generate an analog signal indicative of the x-rays received thereby. The modular radiation detector unit also includes at least one integrated circuit disposed on the circuit board. The integrated circuit includes a plurality of analog to digital conversion channels for converting the analog signals from a plurality of x-ray sensitive cells to digital data.
In accordance with a more limited aspect of the present invention, the plurality of x-ray sensitive cells are arranged in a two-dimensional array having a number of rows and a number of columns.
In accordance with a more limited aspect of the present invention, each row of the two-dimensional array corresponds to a single slice of computerized tomographic image data.
In accordance with a more limited aspect of the present invention, at least one row of the two-dimensional array of x-ray sensitive cells is connected to one integrated circuit.
In accordance with a more limited aspect of the present invention, each analog to digital conversion channel receives analog data from not more than one of the x-ray sensitive cells.
In accordance with a more limited aspect of the present invention, each channel includes a current to frequency converter for generating a number of electrical pulses during a time period. The number of pulses is proportional to the magnitude of the analog signal converted by the channel.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse of the time period.
In accordance with a more limited aspect of the present invention, each channel includes a parallel to serial converter which outputs the first and second digital values in a serial output stream.
In accordance with a more limited aspect of the present invention, the parallel to serial converters are interconnected to generate a serial output of the digital data of a plurality of channels.
In accordance with another aspect of the present invention, a modular radiation detector unit for use in CT imaging is provided. The modular radiation detector unit includes a circuit board, a plurality of x-ray sensitive cells disposed on the circuit board for receiving x-rays after the x-rays have passed through an examination region and for generating analog signals indicative of the x-rays received thereby, and a plurality of integrated circuits disposed on the circuit board and in electrical connection with the x-ray sensitive cells. The integrated circuits include a plurality of channels with each channel being connected with a single x-ray sensitive cell for receiving the analog signal generated by the x-ray sensitive cell and for converting the analog signal to first digital data. The modular radiation detector unit also includes means for receiving second digital data from a second modular radiation detector unit. The second digital data is indicative of the x-rays received at the second modular radiation detector unit. The modular radiation detector unit also includes means for outputting the first and second digital data to a third modular radiation detector unit.
In accordance with a more limited aspect of the present invention, each channel includes a ratiometric current to frequency converter for generating a number of electrical pulses during a time period, the number of pulses being proportional to the magnitude of the analog signal received by the channel.
In accordance with a more limited aspect of the present invention, each channel also includes a frequency to digital converter which generates a first digital value indicative of the number of pulses generated during the time period and a second digital value indicative of a period of time between a first pulse and a last pulse during the time period.
In accordance with a more limited aspect of the present invention, the modular radiation detector unit also includes means to assure that the value of the first digital value is at least two.
In accordance with a more limited aspect of the present invention, each channel also includes parallel to serial converters for outputting the digital data in a serial output stream.
In accordance with a more limited aspect of the present invention, the plurality of x-ray sensitive cells are arranged in a two-dimensional array with each row of the array corresponding to a slice of computerized tomographic image data.
In accordance with a more limited aspect of the present invention, the two dimensional array includes at least thirty-two rows and at least sixteen columns.
In accordance with a more limited aspect of the present invention, each integrated circuit includes at least thirty-two channels.
In accordance with a more limited aspect of the present invention, the integrated circuits are disposed on the circuit board so that the variability of the distances from the x-ray sensitive cells to their respective integrated circuits is minimized.
One advantage of the present invention is that it provides direct digital conversion of radiation signals detected during a CT scan.
Another advantage of the present invention is that it provides a CT system with reduced noise and fictitious data.
Another advantage of the present invention is that it provides a simpler way to convert radiation received in the examination region to digital data.
Another advantage of the present invention is that it provides a more efficient way to process data during multi-slice CT data acquisition.
Another advantage of the present invention is that it provides a simpler cabling system to be used for transferring image data from an examination region to an image processor.
Another advantage of the present invention is that it provides a CT imaging system having x-ray sensitive cells disposed on the same modular assembly as an appropriate number of integrated circuits for generating digital data indicative of the radiation received by the x-ray sensitive cells.
Another advantage of the present invention is that it provides a CT imaging system having radiation detector units whose outputs can be connected to form a single serial stream of digital data for transfer to a remote image reconstruction processor.
Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon a reading and understanding of the following description of the preferred embodiments.